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GEOLOGY OF THE EXPLORATION OF MINERAL RESOURCES OF THE REPUBLIC OF TUVA
Lebedev Vladimir Ilich, Tuvinian Institute for Exploration of Natural Resources of Siberian Branch of RAS, Kyzyl
Email: vil@tikopr. sbras. ru
Abstract. Variety of mineral resources in transboundary areas of Tuva and Mongolia is due to geologic setting of deposits and metallogenic specialization. Mineral resources are characterized by types diversity of natural resources and valuable perspective exploration. Numerous deposits of strategically important and quite deficient sorts of natural resources are explored on the mentioned territory, deposits such as coking and power coal; phosphate and thermal waters; silver-cobalt-arsenic, tantalum-niobium, pyrite-polymetallic, gold-copper-molybdenum porphyry, rare earth carbonatite, lithium, aluminium and chromium ores, as well as gold placers and platinum-group metal placers. Mineral resources exploration potential is retarded by poor transport infrastructure.
Key words: geoecology, Republic of Tyva, geotechnological, uranium deposits, metallogenic provinces, chrysotile-asbestos deposit, metallogenic zones.
Geoecology is a branch of the science studying current state of human habitat for revealing reasons of anthropogenical stress impacts resulted from exploration of natural resources, including mineral resources, on biological diversity of landscape-climatic zones. Geoecology deals with operative control (monitoring) over environment, elaboration of diagnostics methods, study of history of formation of current ecological environments, and prediction of stability and evaluation a degree of natural complex favour for biological functioning.
Under discussion there are problems of geoecology of commercial exploration of mineral resources in the Republic of Tyva. A role of geological processes causing disturbance of natural balance and geochemical cycles, influence of a distribution density, natural erosion, and technogenous disruption on objects, contained heavy and toxic geochemical elements, upon ways of their migration in environments have to be taken into account [2, 3]. A degree of geotechnological and ecological development of deposits for commercial exploration has been evaluated. Retrospective analysis and ■prediction of anthropogenical stress impacts, resulted from conducting geological
works in ore fields of arsenide silver-cobalt, carbonanite, gold-ore, gold placer, rare-earth - rare metal, polymetallic, coal, and chrysotile-asbestos deposits, are given [6]. Ecological advisability of utilization of wastes of "Tuvacobalt" and "Tuvaasbest" plants, Kaa-Khem and Chadan coal pits, and sand-clay refuse of prospector's gold extraction in 1856-1953 have been considered. Data on radioactive pollution of Tuva territory by erosion and prospecting of uranium deposits and nuclear tests at Semipalatinsk (East Kazakhstan) and Lobnor (North-West China) proving grounds have been presented [1].
Famous investigators of South Siberia Z.A. Lebedeva, V. A. Kuznetsov, and P.M. Tatarinov, were the first to call attention in 1930s to the similarity of geological structure of Tuva territory to metallogenic provinces of the "five-element", rare-metal - rare-earth, polymetallic, and precious-metal specialization, traditionally recognized. Subsequently, a probable ore productivity of endogenous and exogenous geological formations, relatively different in age, was theoretically substantiated in works of Yu.A. Bilibin, K.N. Vifanskii, I.I. Abramovich, V.A. Unksov et al. Since the middle 1940s geologists, geochemists, and geophysics of Ermakovskaya, Gornaya, and Berezovskaya expeditions conducted large-scale searches for deposits over more than 40 years. In the course of geological survey and exploration works numerous deposits and ore manifestations of different ore associations have been found on the region territory of the 170.5 thousands square kilometers area. More than 20 large objects of ore and non-ore minerals raw material have been developed for commercial exploration. Among them are Khovu-Aksy arsenide silver-cobalt (five-element) deposit - mined in 1969-1991, Terlig-Khaya barite-cinnabar deposit - ore extracting and output of metallic mercury conducted in 1968-1987, Akdovrak chrysotile-asbestos deposit - explored since 1964, Kaa-Khem and Chadan deposits of energetic and coking coals - explored since 1967 and 1987 respectively. Kyzyk-Tashtyg pyritaceous -polymetallic (in 1964), Karasug iron-rare-earth-barite-fluorite-cabonatite (1957), Uyuk uranium-phosphate (1956), and Ulug-Tanzek tantalum-niobium (1988) deposits were prospected in detail with affirmation reserves in State Committee on Reserves of the USSR. Tastyg deposit of lithium-bearing pegmatites (in 1964), Tardan gold-ore (1979), Aksug copper-molybdenum (1985), and Aryskan yttrium (1989) deposits were preliminary explored with affirmation of reserves. The searches and exploration for placers have been conducted in Amylo-Systygkhem, Kharal-Okhem, Khopto-Tapsa, and Emi gold-bearing districts. Prospecting for aluminum non-bauxite raw material has been conducted within Bayankol massif of alkaline rocks [7].
The objects revealed in Tuva each contain a specific set of toxic elements [1]. Maximum permissible concentrations in soils have been established for these elements: selenium - 0.05 ppm, mercury - 2, cadmium - 3.5, beryllium - 4, molybdenum - 4, antimony - 5, strontium - 10, arcenic - 20, boron - 30, cobalt - 30, chrome - 40, nickel - 50, copper - 60, vanadium - 60, zinc - 70, and lead - 100 ppm.
Although the distribution of anomalous endogenic concentrations is of low density and total area of districts of elevated contents of environmentally dangerous components occupies no more than 0.0001 % of the Tuva territory, the availability of natural stream-forming sources and realms of their accumulation required special ecologo-geochemical studies.
It is well known that Cd, As, Hg, Be, Pb, and Cr are most hazardous for the human habitat. Solis, proluvial-alluvial deposits, and rocks in most of ore regions of Tuva are enriched in these toxic elements. The Ulugoi ore cluster, located on the border between Kaa-Khem and Todzha districts, is a source of Cd and Pb. The Khovu-Aksy (Chedi-Khol district), Ulatai-Choza (Ovyur district), Chergak (Dzun-Khemchik district), Kyzyl-Oyuk, and Askhatiingol (Mongun-Taiga districts) ore fields are sources of As, Sb, Cu, Co, and Ni. The rare-metal and lithium-fluorine deposits of the Sangilen supply Be, B, F, and natural radionuclides U and Th. The chromite-bearing ultrabasic rocks of the Kurtushibinskii (Pii-Khem, Ulug-Khem, and Barun-Khemchik districts), Agardag (Tes-Khem district), Kaa-Khem (Kaa-Khem district) ophiolite belts are sources of Cr and V. The barite-cinnabar ores of the Pel'orug (Terlig-Khaya and Arzak deposits) and Chazadyr-Karasug (Chazadyr deposit) metallogenic zones, mercuric gold of quartz-veined, sulfosalt-sulfide, and copper-molybdemun-porphyric deposits, and products of amalgamation in wastes of sand-clay refuse of prospector's gold mining accumulated from 1856 to date are main sources of Hg in environments of basin complexes. The problem of removal of basin complexes from mercury amalgamation products is urgent [4].
In the course of study of mountainous zones and intermountain basins on the territory of Tuva and adjacent regions of Mongolia, a degree of landscape complexes pollution by heavy metals, toxic elements, and natural and artificial radionuclides has been evaluated [1]. Contents of artificial radionuclides Cs-137 and Sr-90 in soils, forest falling off, and mosses have been determined. The stratifying of their high concentrations suggests that the territory was repeatedly polluted by radionuclides. The geochemical studies of natural complexes permit us to make a conclusion that the most of the Tuva territory is radiation undangerous for human habitat today. Some regularities of anomalous concentration of toxic elements in natural environments have been revealed. Association of anomalous contents of Hg to the basin complexes was most conspicuous. Mercury anomalies have been studied in details with collecting heavy concentrate samples of large volume. It is established that the elevated Hg concentrates in soils, formed upon prospector's working off planted by forest vegetation, follow regenerated gold-bearing placers which magnetite jets in the near-bedrock part of sand-clay refuse are enriched in products of amalgamation with fine and dispersed gold untrapped earlier. The similar feature of mercuric gold concentration in the lower, near bottom, part of the placer-forming dump of adit was established at Kyzyk-Chadr Au-Cu-Mo-porphyric deposit and for a regenerated pay
dirt worked out by system of underground exploitation minings in the bed and lower terrace ridge of the Soruglug-Khem river basin. Technologies and technological complexes for recovery of products of amalgamation and free gold untrapped earlier from sand-clay refuse of old prospector's working off at minimum losses of useful components and compliance with international standard of environment protection have been elaborated in Tuvinian Institute for Exploration of Natural Resources.
More than 86 million cubic meters of removal rocks (chrysotile serpentinites) and wastes of asbestos enrichment were accumulated as a result of commercial exploration of richest chrysotile-asbestos loads of the Aktovrak deposit in the Alash-Khemchic interfluve. It is evident that imperfect extraction of chrysolite-asbestos from serpentinites and intense pollution of agricultural lands and basin complexes of the Khemchik river valley by technogenous wastes have serious environmental impacts. A geotechnology of environmentally safe complex hydro-acid processing of chysotile serpentinites and utilization of wastes of asbestos pneumatic enrichment with production of high value commodity products has been elaborated under direction of V.V. Velinskii. These products are ultra-pure silica gel (silica filler) and amorphous SiO2 for production of fiber glass optics and automobile cord, periclase for lining of open-hearth and steel furnaces, medicine gypsum, unsorted microasbestos for production of superlight heat resistant composite materials, and sulfide-chromite-magnetite concentrate contained elements of platinum group. Technologies for production of magnesium binder being almost as good as Portland cement in quality for use in one-story construction were elaborated in Institute.
A large body of veined mass containing arsenides and sulfides was accumulated in adit dumps of the Khovu-Aksy deposit [4, 5, 6]. More than 1.5 million cubic meters of wastes of hydrometallurgical conversion were stored in burial reservoirs of "Tuvacobalt" Plant. The results of revision works on evaluation of quality and reserves of technological wastes of cobalt production suggest that it is appropriate and required to recovery the wastes. It is established that concentrations of As (3.5-6.4 %), Co (0.14 -0.24 %), Ni (0.15-0.29 %), Bi (0.01-0.02 %), Ag (45 ppm), Cu (0.14 %), Zn (0.11 %), and Au (60 mg per ton) are very high. The burial reservoirs contained more than 2000 ton of Co are an artificial deposit. Hypochlorite-ammoniac-carbonate method and experimental technological equipment for deep processing of enrichment wastes were elaborated in Tuvinian Institute for Exploration of Natural Resources, Siberian Branch of the RAS. It is possible to organize production of high value commodity products (crude Co, Ni, and Cu, cathode Ag, sulfopone, Co salts, and pigments) and recovery of As as thiosulfide and other nontoxic compounds and preparations. We emphasize that more than 50 thousands ton of As environmentally hazard to the basin of the Elegest and Ulug-Khem rivers are accumulated in the burial reservoirs. Ecological catastrophe can occur at washing out the burial reservoirs by showers or destruction as a result of seismic events and so on.
The geoecological state of human habitat and spatial-temporal distribution of heavy metals and toxic elements can be evaluated and reasons of their accumulation and distribution can be analyzed using methods of Earth's sciences. The experience of conducting of geoecological investigation strongly suggests that it is necessary to combine field, stationary, and distant methods for obtaining information about environment changes in response to natural processes of degradation and human activity.
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